To evaluate the protective effect of Ajuga multiflora BUNGE (AMB) extract on the toxicity of lead acetate (LA), environmental pollutant, cell viability was measured by XTT assay using cultured NIH3T3 fibroblasts. And also, the effect of antioxidant, butylated hydroxytoluene (BHT) on LA-induced cytotoxicity was analysed. For the protective effect of AMB extract on LA-induced cytotoxicity, NIH3T3 fibroblasts were pretreated with 80 or 90 μg/mL of AMB extract for 2 hours before the treatment of LA. And also, the antioxidative effects of AMB extract against LA-induced cytotoxicity were assessed by DPPH-radical scavenging activity, superoxide dismutase (SOD)-like activity and inhibitory activity of lipid peroxidation (LP). In this study, LA significantly decreased cell viability dose-dependently compared with control, and then XTT50 value was determined at 46.1 μM of LA. In the effect of BHT against LA-induced cytotoxicity, it effectively prevented toxic effect of LA by the significant increase of cell viability. In the protective effect of AMB extract on LA-induced cytotoxicity, it significantly increased cell viability which was decreased by LA-induced cytotoxicity, and also it showed the antioxidative effects such as DPPH-radical scavenging activity, SOD-like activity and inhibitory activity of LP. From these results, it is suggested that the cytotoxicity of LA is involved in oxidative stress, and AMB extract effectively prevented the cytotoxicity induced by LA via an antioxidative effect. Conclusively, the natural substance such as AMB extract may be alternative resources for the prevention or treatment of diseases related with oxidative stress.